1Preheat oven to 350 degrees. Wash sweet potatoes (or yams) well and place in oven for 35-40 minutes. Allow to cool until you can handle them comfortably. Cut them in half and scoop the insides into a large bowl. Mash. (This should yield about 3 cups.)
2Mix the softened butter, along with the sugar, eggs, vanilla and milk into the sweet potatoes. Transfer to a baking pan or casserole dish.
3Place cream in a small saucepan and bring to a simmer.
Add brown sugar and allow to dissolve. Stir until this mixture reaches the soft ball temp on a candy thermometer. Remove from heat.
4Beat remaining butter and chopped pecans into cream mixture. Once it is well combined, pour over top of mashed sweet potatoes. Bake until hot and just beginning to brown.